TypeInference.java

import java.util.function.Predicate;

public class TypeInference {

    public static void main( String[] args ) {
        // compile
        Pattern<String> p1 = pattern(String.class, expr(s -> s.length() > 3, id("expr1")));
        
        // don't compile
        Pattern<String> p2 = pattern(String.class, expr(s -> s.length() > 3).id("expr1"));
    }

    public static <T> Pattern<T> pattern(Class<T> type, Expr<T> expr) {
        return new Pattern<T>(type, expr);
    }

    public static <T> Expr<T> expr(Predicate<T> pred) {
        return new Expr<T>(pred);
    }

    public static <T> Expr<T> expr(Predicate<T> pred, String id) {
        return new Expr<T>(pred, id);
    }

    public static String id(String id) {
        return id;
    }

    public static class Pattern<T> {
        private final Class<T> type;
        private final Expr<T> expr;

        public Pattern( Class<T> type, Expr<T> expr ) {
            this.type = type;
            this.expr = expr;
        }
    }

    public static class Expr<T> {
        private final Predicate<T> pred;
        private String id;

        public Expr( Predicate<T> pred ) {
            this.pred = pred;
        }

        public Expr( Predicate<T> pred, String id ) {
            this.pred = pred;
        }

        public Expr<T> id(String id) {
            this.id = id;
            return this;
        }
    }
}